This invention relates to a method and composition for cleaning and preserving in a clear condition transparent plastic sheets for example, windows, such as "PLEXIGLAS".
U.S. Pat. Nos. 3,904,732 and 3,677,821 are broadly directed to restoring the surfaces of plastic sheets such as "LUCITE" and "PLEXIGLAS", polymethylmethacrylates.
My invention is more particularly directed to overcoming the problems associated with so-called plastic or synthetic transparent windows such as those windows formulated primarily or entirely from methylmethacrylate.
These windows after a period of time tend to cloud or become less transparent and therefore more opaque. In the cleaning of these windows with the use of commercial cleaners, two problems have been encountered: first, most commercial cleaners, such as are available to consumers at the retail level, will not remove the cloudiness or opaqueness from these windows; second, those few commercial cleaners available that will, in fact, clear the windows, such as "LESTOIL".RTM., a product of Noxell Corporation of Baltimore, Md., will only temporarily restore the transparency.
I have overcome the aforementioned problems of the inability to clean and maintain such windows in a clear or transparent condition by using a two-step process to clear permanently such windows. If the windows are initially clear, then only one of the two steps of my process and formulation is required.
Broadly, my invention comprises cleaning a surface of a transparent methylmethacrylate (a thermoplastic poly-type polymer more specifically an acrylic monomer). Where the acrylic surface is clouded, the first step comprises cleaning the surface to remove the opacity and subsequently coating the cleaned surface to prevent further clouding.
In the first step it has been found that a composition of a petroleum distillate emulsified in water is suitable. The petroleum distillate is a mixture of hydrocarbons having a boiling point between 150.degree.-190.degree. C.; that is, the fraction in the distillation of petroleum between gasoline and the fuel oils as determined in accordance with Standard Method of Tests for Distillation of Gasoline, Naptha, Kerosene and Similar Petroleum Products (ASTM D 86). The petroleum products found in this range are typically referred to as kerosene, coal oil, astrol oil or, more broadly, paraffinic mixtures of hydrocarbons as identified by their boiling point ranges. These paraffinic hydrocarbons may be applied directly in the cleaning step or may be emulsified with water of up to one part hydrocarbon to nine parts water by volume. Alternatively a pine oil-alcohol-water composition may be used such as Pine-Sol a product of American Cyanamid.
In the second step of the process, a coating composition is applied. The coating composition forms a film which permanently adheres to the surface and prevents further clouding. Also, it has been found that the formulations per se will clean the surface but not to the same degree of clearness (clarity) as the combination of both steps. Broadly, the coating composition comprises a polyester resin, such as an alkyd resin. The alkyd resin is modified with an oil such as linseed, safflower, tung, and soy bean, and is further modified or copolymerized with monomers such as urethane, vinyl toluene, acrylic and/or vinyl monomers. The resin is dissolved in a solvent such as petroleum distillates having a boiling point range of between 150.degree. to 190.degree. C. such as mineral spirits and optionally dryers are added which would be compatible with the formulation. The dryers are any compatible oxidant which hastens the drying of the composition, such as a solution of lead, manganese or zinc salts of resin acids.